The specific aims of the proposed research is to define the effects of acute and chronic MDMA ('ecstasy') exposure on serotonin (5-HT) efflux and the functioning of sensory pathways in the mammalian brain using in vivo microdialysis and single unit recordings. The proposed experiments will use the well-defined rat trigeminal somatosensory system as a model to assess the effects of MDMA during acute and chronic exposure on the functioning of the somatosensory system. These experiments will test the hypothesis that acute and chronic MDMA results in alterations of 5-HT efflux and significant changes in the responsiveness of single sensory neurons to afferent information. Characterizing the acute and chronic effects of MDMA will contribute to our understanding of its popularity as a recreational drug. In addition, these experiments will lead to a better understanding of the physiological mechanisms underlying MDMA's effects on tactile information processing. Taken together, this will advance our knowledge of certain phenomena associated with MDMA administration including behavioral sensitization, tolerance, and drug relapse all of which involve sensory processes and contributes to MDMA's abuse liability.